[enhancement] set config directory from cli

[GoogleCodeExporter]

I'd like to use comictagger on a synology NAS, and I want to create a package 
to easily install it.
The nas runs a custom gnu/linux os, with a particular file structure, and it 
would be great to have a command line argument to tell comictagger what is the 
folder for config files(like the -c command line argument for transmission)

Original issue reported on code.google.com by ander.ba...@gmail.com on 6 Jan 2015 at 11:12